Full coverage of a second generation (2G) or third generation (3G) network such as Global System for Mobile Communications (GSM) or Wideband Code Division Multiple Access (WCDMA) has been basically implemented.
With development of Long Term Evolution (LTE) network technologies, LTE networks have covered some urban areas and traffic hot spot areas. In this way, on current communication networks, the LTE networks coexist with the 2G or 3G network.
During a call, user equipment (UE) may enter a 2G or 3G network from an LTE network, and handover from a packet switched (PS) domain to a circuit switched (CS) domain is required due to different bearer mechanisms of the LTE network and the 2G or 3G network, where interruption of a voice call may occur, and consequently, continuity of the voice call of a user is affected.
Circuit switched fallback (CSFB) is that when user equipment (UE) covered by LTE network processes a voice service, the UE first falls back to a network that has a CS domain, and processes the voice service on the network that has a CS domain, thereby fulfilling an objective of reusing an existing CS domain device to provide a traditional voice service for a user on the LTE network. In the prior art, in a process of implementing CSFB, handover of UE from an LTE network to a CS domain of a 2G or 3G network is triggered, which reduces an access delay of accessing the CS domain of the 2G or 3G network by the UE, thereby also improving user experience.
In the prior art, for a call in which UE is a called party by means of CSFB, the UE moves from an LTE network to a 2G or 3G network after receiving the call, and then generates a voice session according to a called procedure to perform talking. As a result, a user waits a long time for a voice session to be connected, thereby easily leading to on-hook of the user, and causing failure of the call.